1. Field of the Invention
The present invention relates to an image forming device comprising a photoreceptor such as a laser printer etc.
2. Description of the Related Art
A laser printer forms an image on a printing sheet by transferring a developer developed on a photoreceptor onto the printing sheet. Some laser printers comprise a belt disposed so as to face the photoreceptor. This belt may be used to convey the printing sheet while causing the printing sheet to contact the photoreceptor. As the printing sheet is conveyed while contacting the photoreceptor, the developer is transferred onto the printing sheet from the photoreceptor. In the present specification, a belt for conveying a print medium (printing sheet or the like) will be referred to as a conveyor belt.
Furthermore, a belt is known which contacts the photoreceptor such that the developer is transferred onto the belt from the photoreceptor. The printing sheet contacts a part of the belt on which the developer has been transferred. The developer is thus transferred onto the printing sheet from the belt. In this technique, a primary transfer from the photoreceptor to the belt and a secondary transfer from the belt to the printing sheet are performed. In the present specification, a belt used in an image forming device which adopts this technique of performing the primary transfer and the secondary transfer will be referred to as an intermediate transfer belt.
Paper particles of the printing sheet adhere to the conveyor belt. If the paper particles remain on the conveyor belt, the printing quality may deteriorate. Further, an image forming device is known which evaluates the concentration of the developer by transferring the developer from the photoreceptor to the conveyor belt on a trial basis. Further, developer may adhere to the conveyor belt during a paper jam. If the developer remains on the conveyor belt, the printing sheet is stained when the conveyor belt conveys the printing sheet. Therefore, the conveyor belt must be cleaned to remove the paper particles and developer.
There is a possibility that the developer transferred onto the intermediate transfer belt during the primary transfer is not transferred entirely onto the printing sheet during the secondary transfer. If developer remains on the intermediate transfer belt, this developer may be transferred onto the printing sheet. In this case, the developer is transferred onto unintended parts of the printing sheet, and this causes deterioration of the printing quality. Therefore, the intermediate transfer belt must be cleaned to remove the developer not having been transferred to the printing sheet in the secondary transfer.
As described above, when the conveyor belt or the intermediate transfer belt is used, the belt must be cleaned. US Patent Application Publication NO. 2005/0074250 discloses a technique for cleaning the belt. This technique adopts a back roller disposed on the back side of the belt and a front roller disposed on the front side of the belt. The front roller faces the back roller. In this technique, a constant voltage is applied between the back roller and front roller. The paper particles and developer adhered to the belt move to the front roller by an electric field generated between the back roller and front roller. The paper particles and developer are thus trapped on the front roller, and the belt is cleaned.